From 87037106b23e9289844eeed73c787122c56df7ac Mon Sep 17 00:00:00 2001
From: Daisuke Oyama <oyama@e.u-tokyo.ac.jp>
Date: Sun, 4 Nov 2018 14:02:43 +0900
Subject: [PATCH] Add NormalFormGame.delete_action

---
 quantecon/game_theory/normal_form_game.py     | 58 +++++++++++++++++++
 .../tests/test_normal_form_game.py            | 33 +++++++++++
 2 files changed, 91 insertions(+)

diff --git a/quantecon/game_theory/normal_form_game.py b/quantecon/game_theory/normal_form_game.py
index 409f6ff09..fcb4a4681 100644
--- a/quantecon/game_theory/normal_form_game.py
+++ b/quantecon/game_theory/normal_form_game.py
@@ -727,6 +727,64 @@ def __setitem__(self, action_profile, payoff_profile):
                 tuple(action_profile[i:]) + tuple(action_profile[:i])
             ] = payoff_profile[i]
 
+    def delete_action(self, player_idx, action):
+        """
+        Return a new `NormalFormGame` instance with the action(s)
+        specified by `action` deleted from the action set of the player
+        specified by `player_idx`. Deletion is not performed in place.
+
+        Parameters
+        ----------
+        player_idx : scalar(int)
+            Index of the player to delete action(s) for.
+
+        action : scalar(int) or array_like(int)
+            Integer or array like of integers representing the action(s)
+            to be deleted.
+
+        Returns
+        -------
+        NormalFormGame
+            Copy of `self` with the action(s) deleted as specified.
+
+        Examples
+        --------
+        >>> g = NormalFormGame(
+        ...     [[(3, 0), (0, 1)], [(0, 0), (3, 1)], [(1, 1), (1, 0)]]
+        ... )
+        >>> print(g)
+        2-player NormalFormGame with payoff profile array:
+        [[[3, 0],  [0, 1]],
+         [[0, 0],  [3, 1]],
+         [[1, 1],  [1, 0]]]
+
+        Delete player `0`'s action `2` from `g`:
+
+        >>> g1 = g.delete_action(0, 2)
+        >>> print(g1)
+        2-player NormalFormGame with payoff profile array:
+        [[[3, 0],  [0, 1]],
+         [[0, 0],  [3, 1]]]
+
+        Then delete player `1`'s action `0` from `g1`:
+
+        >>> g2 = g1.delete_action(1, 0)
+        >>> print(g2)
+        2-player NormalFormGame with payoff profile array:
+        [[[0, 1]],
+         [[3, 1]]]
+
+        """
+        # Allow negative indexing
+        if -self.N <= player_idx < 0:
+            player_idx = player_idx + self.N
+
+        players_new = tuple(
+            player.delete_action(action, player_idx-i)
+            for i, player in enumerate(self.players)
+        )
+        return NormalFormGame(players_new)
+
     def is_nash(self, action_profile, tol=None):
         """
         Return True if `action_profile` is a Nash equilibrium.
diff --git a/quantecon/game_theory/tests/test_normal_form_game.py b/quantecon/game_theory/tests/test_normal_form_game.py
index f64f2a634..057f36bf9 100644
--- a/quantecon/game_theory/tests/test_normal_form_game.py
+++ b/quantecon/game_theory/tests/test_normal_form_game.py
@@ -209,6 +209,17 @@ def test_getitem(self):
         assert_array_equal(self.g[action_profile],
                            self.BoS_bimatrix[action_profile])
 
+    def test_delete_action(self):
+        action_to_delete = 0
+        for i, player in enumerate(self.g.players):
+            g_new = self.g.delete_action(i, action_to_delete)
+            actions_to_remain = \
+                np.setdiff1d(np.arange(player.num_actions), action_to_delete)
+            assert_array_equal(
+                g_new.payoff_profile_array,
+                self.g.payoff_profile_array.take(actions_to_remain, axis=i)
+            )
+
     def test_is_nash_pure(self):
         ok_(not self.g.is_nash((1, 0)))
 
@@ -239,6 +250,17 @@ def setUp(self):
     def test_getitem(self):
         assert_array_equal(self.g[0, 0, 1], [6, 4, 1])
 
+    def test_delete_action(self):
+        action_to_delete = 0
+        for i, player in enumerate(self.g.players):
+            g_new = self.g.delete_action(i, action_to_delete)
+            actions_to_remain = \
+                np.setdiff1d(np.arange(player.num_actions), action_to_delete)
+            assert_array_equal(
+                g_new.payoff_profile_array,
+                self.g.payoff_profile_array.take(actions_to_remain, axis=i)
+            )
+
     def test_is_nash_pure(self):
         ok_(self.g.is_nash((0, 0, 0)))
         ok_(not self.g.is_nash((0, 0, 1)))
@@ -382,6 +404,17 @@ def test_getitem(self):
         """Trivial game: __getitem__"""
         eq_(self.g[0], 0)
 
+    def test_delete_action(self):
+        actions_to_delete = [1, 2]
+        for i, player in enumerate(self.g.players):
+            g_new = self.g.delete_action(i, actions_to_delete)
+            actions_to_remain = \
+                np.setdiff1d(np.arange(player.num_actions), actions_to_delete)
+            assert_array_equal(
+                g_new.payoff_profile_array,
+                self.g.payoff_profile_array.take(actions_to_remain, axis=i)
+            )
+
     def test_is_nash_pure(self):
         """Trivial game: is_nash with pure action"""
         ok_(self.g.is_nash((1,)))